A known method for producing a fragranced air stream is described in U.S. Pat. No. 2,410,488. In that case a strip-like fragrance carrier is moved forward and back in the interior of an evaporation shaft, while a stream of fresh air flows through the evaporation shaft.
In known fragrancing devices, the fragrance is admixed by exposing fragrance gel or fragrance granules in a stream of fresh air. The fragranced fresh-air stream is then either passed directly into a room to be fragranced or supplied to an air-supply or air-conditioning system, so that the fragrance can be dispersed into the rooms connected thereto.
The use of such fragrancing devices usually leads very rapidly to reduction of the quality of the produced fragranced-air stream by demixing at surfaces and oxidation. Particular difficulties are already encountered in changing the fragrance, since this is successful only when the entire equipment has been thoroughly cleaned to eliminate all residues of the previously used fragrance.
For better understanding of the relationships and causes, it will be assumed that the fragrances used for fragrancing of rooms are most usually complex mixtures of ethereal oils, such as orange oil, peppermint oil, etc. and individual fragrances. The latter are optionally fragrances that are natural, identical to natural, semisynthetic or completely synthetic, for example from geraniol, menthol, Cedramber, galaxolide, etc.
In total, approximately 3000 fragrance components are available to the perfumer as the person skilled in the art of fragrance mixtures. These are characterized by different evaporation temperatures and rates, fragrance intensities, oxidation resistances, duration of action, etc.
Despite relatively short maintenance intervals, surfaces coming into contact with the fragrance, especially in the vicinity of the dosing device or of flow ducts, lead to disadvantageous coatings, for example due to resinification of fragrance residues or due to sooting with liquid residual components of the arriving fragranced air. In many cases the fresh aromas are already masked or demixed after a few hours, and instead fragrance residues creating a stale and depleted impression escape. Maintenance intervals that are too long very rapidly lead to contamination of entire ventilation systems, often caused by use of sprays as dosing devices. On the other hand, no improvement is achieved even by overdosing the fragrance concentrations introduced into a ventilation system. To the contrary, the consequence is overstimulation of the sensory perception in people who spend time in the fragranced room, frequently accompanied by headaches.
It is self-evident that spontaneous changes of fragrance are ineffective in contaminated ventilation systems, since the deposited fragrance droplets are still released to the arriving fresh air hours or even days later, with the unpleasant consequence that indefinable fragrance mixtures are formed after a change of fragrance.